One class of conventional semi-resonant power converter circuits includes high-side (such as control switch circuitry) and low-side switches (synchronous switch circuitry) that transfer power from an input source to a tapped inductor that supplies output power to a load. In such conventional semi-resonant power converter circuits, a tapped inductor is also connected to a second low-side switch, namely, a synchronous rectification (SR) switch.
In order to meet the power requirements for a load of a semi-resonant converter (e.g., provide a near constant output voltage for the load), many conventional semi-resonant DC-DC converters employ a variable switching frequency in which a respective switching period of each phase varies from cycle to cycle. During a portion of each switching period, the SR switch is enabled such that current flows through it. For the semi-resonant converter described above, the current during this portion of a switching period will be shaped like one half cycle of a sinusoidal period. The time interval for this half-cycle sinusoid is determined by reactive elements within passive circuitry of the semi-resonant converter, e.g., the natural resonant frequency of an inductor/capacitor (LC) resonant tank and other passive components within the semi-resonant DC-DC converter determine this time interval.
In order to minimize voltage and current ripple at the output of a voltage converter and to scale up its power output, a voltage converter may make use of multiple phases. The phases are each, effectively, separate voltage converters wherein each is tied to a common input voltage source and powers a common output load. To maintain stability and minimize the ripple, the phases should be driven by a common switching frequency, but with the switch control signals to each of the phases staggered in time.